Blade for a gas turbine and casting technique method for producing same

ABSTRACT

A blade for a gas turbine has a leading edge and a trailing edge, and an interior cavity, which is delimited by internal surfaces, for guiding cooling air therethrough. A multiplicity of turbulators or pins, which are formed on the wall, are arranged in a distributed manner in the region of the trailing edge and project from the internal surfaces into the cavity, to improve the transfer of heat between the wall of the blade and the cooling air. An improvement of the internal cooling is achieved by the turbulators or pins extending into the cavity in a direction which can be freely selected within an angular range.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/961.659, filed on Dec. 7, 2010, which is a continuation of Int. App.No. PCT/EP2009/056150, filed on May 20, 2009, which claims priority toSwiss App. No. 00898/08, filed on Jun. 12, 2008 the entire contents ofwhich are incorporated by reference herein.

FIELD OF INVENTION

The present invention relates to the field of gas turbine technology. Itrefers to a blade for a gas turbine and a method for producing such ablade by a casting technique.

BACKGROUND

Blades of gas turbines, which are fastened either as rotor blades on therotor or fastened as stator blades on the casing which encloses therotor, are subjected to impingement by hot gas which comes from thecombustor and are exposed to thermal loads in the process. These blades,in the course of improving the thermal efficiency, are increasinglyexposed to circumferential flow at still higher turbine inlettemperatures. It is not to be ignored, therefore, that these blades haveto be cooled internally and/or externally by a cooling medium,especially cooling air, being introduced preferably via the blade rootinto the hollow interior of the blade airfoil, cooling the bladeinternally there via convectively applied cooling methods or selectivelyby means of impingement cooling, and then being blown out into the hotgas flow, in order to carry out a so-called film cooling there ifnecessary on the external side of the blade. The cooling medium flowsthrough the interior of the blade mostly in a plurality of coolingpassages which are connected in a serpentine-like manner and extendthrough the blade airfoil in the radial direction.

When producing such a blade by a casting technique, a casting core,which forms and keeps the internal hollow cavity of the blade with thecooling passages free and further details during the casting of theblades, has to be created. For producing the casting core, use is madeof a core mold assembled from two halves which during demolding of thefinished casting core are drawn apart in a specified direction (see U.S.Pat. No. 5,716,192, for example). Contingent upon the direction in whichthe two mold halves have to be drawn apart, limitations ensue in thedesign of the casting core and therefore in the design of the cavity ofthe subsequent blade. These limitations play a role particularly in thecase of complex shapes of the cavity, as are described inWO-A1-03/042503, for example. In order to create the cavity of the bladethere, which cavity consists of various cooling circuits and amultiplicity of pins and turbulators, a plurality of casting cores areproduced and combined with each other, which leads to a very costlyproduction process.

SUMMARY

In a first aspect, the present disclosure is directed to a blade for agas turbine. The blade includes a leading edge and a trailing edge, andan interior cavity, which is delimited by internal surfaces, for guidingcooling air therethrough. To improve the transfer of heat between thewall of the blade and the cooling air, a multiplicity of members, whichare formed on the wall to improve cooling. The members are arranged in adistributed manner in the region of the trailing edge and project fromthe internal surfaces into the cavity. The members extend into thecavity in a direction which can be freely selected within an angularrange.

In a second aspect, the present disclosure is directed to method forproducing the above blade. The method includes, in a first step,providing a core mold for forming a casting core which keeps the cavityof the blade free. The method also includes, in a second step, producingthe casting core by means of the core mold, in a third step, removingthe casting core from the core mold and, in a fourth step, casting theblade by the casting core. The core mold which is provided in the firststep comprises two mold halves, which during demolding are drawn apartin a first direction. At least one mold insert, which is provided forforming the members, is arranged in the mold halves in the trailing edgeregion. In the third step, after the parting of the mold halves in thefirst direction, the at least one mold insert is withdrawn from theformed casting core in a second direction which differs from the firstdirection.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall subsequently be explained in more detail based onexemplary embodiments in conjunction with the drawing. All elementswhich are not essential for the direct understanding of the inventionhave been omitted. Like elements are provided with the same designationsin the various figures. In the drawings:

FIG. 1 shows in cross section in a greatly simplified view an exemplaryembodiment of a blade according to the invention with turbulators orpins which project into the cavity perpendicularly to the wall surfacein the region of the trailing edge;

FIG. 2 shows in section the simplified casting core for producing theblade from FIG. 1 by a casting technique;

FIG. 3 shows the problems which are associated with the mold halves ofthe core mold when producing the casting core from FIG. 2;

FIG. 4 shows in a view which is comparable to FIG. 3 a core mold, whichis modified within the scope of the invention, with mold inserts forovercoming the limitations which are associated with the core moldaccording to FIG. 3, and

FIG. 5 shows one of the mold inserts from FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Introduction to theEmbodiments

The invention should provide a remedy here. It is therefore an object ofthe invention to propose a blade which is improved with regard tointernal cooling, overcoming certain limitations created by the castingcore, and which at the same time can be produced with little additionalcost. It is furthermore an object of the invention to disclose a methodfor producing such a blade.

The object is achieved by means of the entirety of the features of theindependent claims. It is a feature of the invention that theturbulators or pins which are formed on the wall in the region of thetrailing edge for improving the heat transfer between the wall of theblade and the cooling air extend into the cavity in a direction whichcan be freely selected within an angular range.

With regard to the cooling, it is particularly advantageous if,according to one development of the invention, the turbulators or pinsextend into the cavity in a direction which is essentially perpendicularto the associated internal surface.

The method according to the invention for producing the blade by acasting technique, in which, in a first step, a core mold is providedfor forming a casting core which keeps the cavity of the blade free, ina second step, the casting core is produced by means of the core mold,in a third step, the casting core is removed from the core mold, and ina fourth step, the blade is cast by means of the casting core. The coremold, which is provided in the first step, comprises two mold halveswhich during demolding are drawn apart in a first direction, wherein atleast one mold insert, which is provided for forming the turbulators orpins, is arranged in the mold halves in the trailing edge region, and inthe third step, after the parting of the mold halves in the firstdirection, the at least one mold insert is withdrawn from the formedcasting core in a second direction which differs from the firstdirection.

In one development of the method according to the invention, the seconddirection is perpendicular to the internal surface which is associatedwith the turbulators or pins.

According to another development of the method, a plurality of moldinserts are arranged in the mold halves and during demolding of theformed casting core are withdrawn in different directions which differfrom the first direction.

DETAILED DESCRIPTION

FIG. 1 shows, in cross section in a greatly simplified view, anexemplary embodiment of a gas turbine blade according to the invention.The blade 10 has an airfoil profile with a leading edge 11, a trailingedge 12 and also a (convex) suction side 13 and a (concave) pressureside 14. The blade 10 has a wall 15 which encloses a hollow cavity 16which is used for the guiding of cooling air which inter alia candischarge into the outside space from cooling air outlets 17 which areprovided at the trailing edge 12. The cavity 16 can be divided into aplurality of sub-chambers by means of one or more ribs 29.

For forming the cavity 16 and the details and elements which arearranged therein, a casting core 21 (FIG. 2), which has to be producedin advance, is required when producing the blade 10 by a castingtechnique. For producing the casting core 21, use is made as a rule of acore mold 23 according to the type shown in FIG. 3, which is assembledfrom two mold halves 23 a and 23 b which can separated along a partingplane 25 and which during demolding are drawn apart in the directionwhich is indicated by the arrows in FIG. 3. As a result of the specifieddirection, in which the two mold halves 23 a and 23 b have to be drawnapart during demolding (demolding direction), the orientation ofspecific elements in the cavity 16 of the blade is also indirectlydetermined via the casting core 21. Thus, the rib 29 in the cavity 16 ofthe blade extends inevitably in the demolding direction because the moldhalves 23 a and 23 b with their corresponding rib elements 30 can onlybe withdrawn from the finished casting core in this way.

According to the invention, additional elements 18 in the cavity, whichcan be formed as (round) pins or (rib-like) turbulators and improve thetransfer of heat between the cooling air which flows in the cavity 16and the wall 15, are now arranged or formed in the trailing edge regionof the blade 10. The direction in which the elements 18 project from thewall 15 into the cavity 16 should now be able to be selected within anangular range independently of the demolding direction of FIG. 3, i.e.the orientation of the elements 18 can differ from the orientation ofthe rib 29. In particular, the elements 18, for fluidic reasons, areintended to be perpendicular to the internal surface 19 or 20 of thewall from which they extend, as is indicated by the right angle in FIG.1.

In order to be able to realize the elements 18 from FIG. 1 with theorientation which is shown there, the casting core 21 would have to havecorrespondingly formed and oriented recesses 22 (FIG. 2). In the case ofthe two-part core mold 23 of FIG. 3, corresponding mold elements 26would have to be arranged on the mold halves 23 a and 23 b for formingthe recesses 22. However, it is immediately apparent in the view of FIG.3 that in the case of mold elements 26 which are differently orientatedin such a way the two mold halves 23 a and 23 b during demolding can nolonger be drawn apart in the demolding direction without the formedrecesses 22 being damaged or being destroyed, or the mold elements 26being sheared off.

In order to be able to create such differently oriented elements 18 in asimple manner and without the risk of damage within the productionprocess for the casting core 21, however, according to FIGS. 4 and 5provision is made for separate mold inserts 27, 28 for the region inwhich the elements 18 are to be arranged, which mold inserts areresponsible for forming the recesses 22 and can be withdrawn separatelyfrom the mold halves 23 a and 23 b.

During the production of the casting core 21 with a core moldconfiguration according to FIG. 4, the mold halves 23 a and 23 b, duringdemolding, are first of all drawn apart in the demolding direction(vertically upwards and downwards in FIG. 4). The mold inserts 27 and 28remain on the casting core 21 in this phase. If the mold halves 23 a and23 b are removed, the mold inserts 27 and 28 can be withdrawn from thecasting core in those directions which correspond to the orientation ofthe elements 18 (inclined arrows in FIG. 4). In this way, it is possiblewithin the scope of the customary casting process to create in a simpleway elements 18 in the cavity 16 of the blade 10 which are optimized forcooling and the orientation of which differs from the (main) demoldingdirection of the core mold.

LIST OF DESIGNATIONS

-   10 Blade (gas turbine)-   11 Leading edge-   12 Trailing edge-   13 Suction side-   14 Pressure side-   15 Wall-   16 Cavity-   17 Cooling air outlet-   18 Turbulator (pin)-   19, 20 Internal surface-   21 Casting core-   22 Recess-   23 Core mold-   23 a, b Mold halves-   24 Cavity-   25 Parting plane-   26 Mold element-   27, 28 Mold insert-   29 Rib-   30 Rib element

What is claimed is:
 1. A method for producing a blade for a gas turbineby a casting technique, the blade having a leading edge and a trailingedge, and an interior cavity, which is delimited by internal surfaces,for guiding cooling air therethrough, wherein for improving the transferof heat between the wall of the blade and the cooling air, amultiplicity of members, which are formed on the wall to improvecooling, are arranged in a distributed manner in the region of thetrailing edge and project from the internal surfaces into the cavity,the members extending into the cavity in a direction which can be freelyselected within an angular range, the method comprising: providing acore mold for forming a casting core which keeps the cavity of the bladefree; producing the casting core by means of the core mold; removing thecasting core from the core mold; and casting the blade by the castingcore, wherein: the provided core mold comprises two mold halves, whichduring demolding are drawn apart in a first direction; at least one moldinsert, which is provided for forming the members, is arranged in themold halves in the trailing edge region, and in the removing of thecasting core from the core mold, after the parting of the mold halves inthe first direction, the at least one mold insert is withdrawn from theformed casting core in a second direction which differs from the firstdirection.
 2. The method as claimed in claim 1, wherein the seconddirection is perpendicular to the internal surface which is associatedwith the members.
 3. The method as claimed in claim 2, wherein aplurality of mold inserts are arranged in the mold halves and duringdemolding are withdrawn from the formed casting core in differentdirections which differ from the first direction.